A switch device plays an important role in a circuit, which functions to connect or disconnect the circuit. When the circuit is disconnected by the switch device, a switch tube generates an arc, and the arc dramatically raises the temperature of the members such as contacts in the switch tube, and even results in the loss of the members. Particularly, in a high voltage circuit, the intensity of the arc, which is generated when the circuit is disconnected, is rather high, and as a result, the service life of the switch tube is greatly shortened. Therefore, the arc-extinguishing must be performed for the switch tube in the ON/OFF process of the circuit.
In the prior art, an arc-extinguishing medium such as oil, sulfur hexafluoride (SF6), air, semiconductor, or vacuum is usually used for arc-extinguishing in the switch device. Different arc-extinguishing media have different characteristics, and are suitable for the arc-extinguishing of circuit switches with different voltages. As the vacuum switch has small gaps, high voltage-resistant capability, low arc voltages, high current breaking capability, low electrical erosion, and long electrical endurance, the vacuum switch has been widely applied in high-voltage power circuits.
When the switch tube is disconnected, a contact area of contacts at two ends of the switch gradually decreases, until only one contact point is left between the contacts. At the same time, a contact resistance gradually increases, such that a temperature of an area where the contact point is located gradually rises. Once the temperature is higher than a melting point of the contact point, the contact point is melted, evaporated, and ionized. The metal vapor maintains the discharging in vacuum, so as to generate a vacuum arc. At the instant when the contacts are disconnected, flame-like cathode spots are formed on the contact surfaces, and thus eventually the contacts are electrically disconnected.
In the prior art, the contacts in the vacuum switch tube are usually column bodies. A magnetic member and a conductive member are disposed in each contact. When the switch is disconnected, the contact area of the contacts at two ends of the switch device gradually decreases, until only one contact point is left between the contacts. At the same time, the contact resistance gradually increases, such that the temperature of the area where the contact point is located gradually rises. Once the temperature is higher than the melting point of the contact point, the contact point is melted, evaporated, and ionized. The metal vapor maintains the discharging in vacuum, so as to generate a vacuum arc. At this time, the key point of the successful current breaking is that an insulation recovery speed at the gaps of the contacts is higher than a transient recovery voltage speed at the gaps of the contacts after the zero crossing of the arc current, such that re-ignition does not occur and the current breaking is successful. During the current breaking in the vacuum arc-extinguishing chamber, the metal vapor released by the arc diffuses rapidly during the zero crossing of the arc current and is condensed instantly upon encountering the contacts or surfaces of shielding case. However, in the current vacuum switch tube, due to the restriction of structural shapes of the contacts, it is usually very difficult to form a desirable vertical magnetic field for performing arc-extinguishing, and it is rather difficult to solve problems such as electric field concentration, insufficient voltage resistance and etc. during the high voltage breaking process. For a high voltage circuit, the 36-kilovolt voltage breaking can be realized in the prior art. For a higher voltage circuit, particularly, 72-kilovolt high voltage circuit, currently, no vacuum switch tube structure is available for satisfying effective arc-extinguishing requirements during the breaking process. This is one of the problems to be solved in the vacuum switch technology in the prior art.